Briana Williams of Jamaica crosses the finish line to win gold in the final of the women’s 100m at the IAAF World U20 Championships on Jul. 12, 2018 in Tampere, Finland. (Photo by Charlie Crowhurst/Getty Images for IAAF)

Briana Williams arrived at the World U20 Championships earlier this year as an underdog. Then she won the women’s sprint double at the impressively-young age of 16. When Henry Cejudo squared up then-UFC Flyweight champ Demetrious Johnson in August, he, too, was rated the underdog. But Cejudo would snap Johnson’s 11-match streak of title defenses. Behind the scenes, those upsets were linked by a single piece of technology: a clinical-grade device that told Williams and Cejudo exactly how hard to push in training sessions and when to takes rests.

That device, the Humon Hex, measures muscle oxygen use in real time to get a read on ...